This invention relates to an engine valve actuating system and more particularly to an improved arrangement for achieving variable valve actuation (timing and/or lift) in the operation of an engine valve. In addition the invention relates to an improved lash adjustment arrangement useable in engine valve actuation.
As is well-known, many factors in an internal combustion engine represent a design compromise. Generally, the compromise is between achieving good low-speed performance and economy and high output and high power. There has been proposed a wide variety of devices, however, so as to permit the engine characteristics to be adjusted during its running, so as to obtain improved performance across the entire speed and load range. One of these features is variable valve actuation which includes both changing the valve timing and/or the valve lift. Obviously, these present substantial challenges to the engineer considering that the adjustment must be made when the engine is running.
A wide variety of mechanisms have been proposed for achieving either or both of the variable valve timing and variable valve lift. For the most part, however, they are fairly complex and add significantly to the complexity of the valve train.
It was, therefore, a principal object of our earlier invention to provide an improved variable valve actuating mechanism that was relatively simple in construction and which lent itself to incorporation in multi-valve engines.
This was achieved by providing a valve operating mechanism comprised of a single cam shaft having a pair of adjacent cams. A pair of adjacent, pivotally supported rocker arms, each cooperated with a respective one of the cams. A first of the rocker arms had an operating portion for direct cooperation with the valve stem for operating the valve. Means provided a selective coupling of the second rocker arm to the first rocker arm for effecting actuation of the valve through the first rocker arm. Thus, by providing different characteristics of the cam and rocker arms, varying lift and/or duration was achieved.
In order to provide the coupling between the first and second rocker arms and to adjust for wear and other conditions, a mechanism was provided for permitting adjustment in the relationship between the two rocker arms. This utilized a conventional type of adjusting screw.
The use of the adjusting screw somewhat complicates the overall valve mechanism and further requires sufficient clearances so that the screw can be adjusted and so that the relative movement between the rocker arms can be accommodated.
It is, therefore, a principal object of this invention to provide an improved construction of this type wherein the interrelationship between the two rocker arms is simplified while adjustment potential is still maintained.